1. Field of the Invention
The present invention relates to a method and an apparatus for designing structures of molds by converting product data to solids using a 3-dimensional CAD system. More particularly, the present invention relates to a method for dividing each mold into two parts (cavity and core) when molds are designed using a 3-dimensional CAD system.
2. Description of the Prior Art
Generally, as shown in FIGS. 20 to 23, when a 3-dimensional CAD system is used for designing molds, a product solid (3-dimensional shape model data of an object product, created by a computer) (A') (see FIG. 20) is put in a mold block solid (D') such as a rectangular solid, which is equivalent to a nesting in a mold base, then removed from the mold block solid, thereby to form a cavity (E') to become a product (an object formed with resin in the mold) in the mold block solid (FIG. 21). Then, the mold block solid is divided into upper and lower parts at this cavity assumed as a boundary, thereby to form a cavity solid (F') and a core solid (G') (FIG. 23). This dividing, however, includes many restrictions and problems when performed on a 3-dimensional CAD system. In other words, any of present CAD systems cannot cut such a mold block solid partially. When a mold block solid is cut unavoidably using such a present CAD system, therefore, the solid must be cut completely on its entire surface and then portions that should have not been cut must be put together after they are cut.
At present, for example, a general method for dividing such a mold block solid divides a rectangular solid along the cavity described above. In this case, at first, a surface (J) is added along a mold parting line and extended, thereby to divide the rectangular solid. The rectangular solid is thus divided all along the parting line of the mold repetitively (FIG. 22). After this, necessary portions are put together, thereby to generate a cavity solid (F') and a core solid (G') finally to design the object mold (FIG. 23).
A method for manufacturing molds using a 3-dimensional CAD system such way is disclosed in the official report of Unexamined Published Japanese Patent Application No. 8-4854 "Method for Manufacturing Molds". The technology disclosed in the patent applies only to very simple structured molds to be divided only at a reference parting line (2) respectively. The technology does not disclose anything about a method for dividing a mold into a cavity and a core when the mold is designed for a complicated shape product.
When in designing a mold using a 3-dimensional CAD system described above in the prior art method for dividing molds, a surface is extended as shown in FIG. 22 and a portion (K) that should not be divided is also divided. And, when such a dividing is repeated, a rectangular solid is divided into many models. Furthermore, generally, there are very few of simple structured molds, each of which is divided at a reference parting line as disclosed in the official report of Unexamined Published Japanese Patent Application No. 8-4854. In many cases, molds are very complicated in structure and each of them has many parts (parting positions). Each of those molds is divided into a cavity and a core by repeating such the dividing of parts. Consequently, the more a mold is complicated in structure, the more the time and labor for dividing parts of the mold are needed.
Furthermore, in the prior art dividing method, when such a sharp shape (N) as a junction between an arc (L) and a surface (M) is left as shown in FIG. 24, the mold cannot be divided. In addition, since it is difficult to divide the mold on a free curved surface and many dividing and sewing operations are needed, the accuracy of product solid data itself is degraded.